This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Abnormalities of AF volume may have significant consequences for fetal growth and development even in the absence of fetal structural abnormalities. The mechanisms responsible for the maintenance of homeostasis of AF volume and composition are of critical importance to healthy fetal growth and development. However, the known regulatory mechanisms (fetal urine, lung liquid, swallowing) do not explain the results observed. One candidate for an alternative regulatory mechanism is the intramembranous (IM) pathway through the fetal membranes, with absorption of water into the fetal circulation. As water and electrolyte flow through the fetal membranes is crucial to maintenance of AF homeostasis, and water flow through many biological membranes is regulated by AQP water channels, the presence of water channels in the fetal membranes suggests that the AQP family of water channels contributes importantly to IM flow.